The present invention relates to a loudness volume control system for an audio device.
In an audio system, when the volume is small, low and high frequency ranges are insufficient because of the characteristic of auditory sensation. Therefore, a volume control system in the audio system is provided with a function for changing a frequency characteristic in accordance with a volume position as a loudness volume control system.
FIG. 8 shows a well-known example of the frequency characteristic of the auditory sensation by Robinson et al. In FIG. 8, each line shows a sound pressure level of a pure sound which a man having a normal auditory sensation feels as a sound at the same volume over an audio frequency.
FIG. 9 shows a conventional loudness volume control system having a tap. The control system comprises a variable resistor VR having an end a connected to a signal input terminal IN, a center tap b, and the other end c connected to the ground. A slider d connected to a signal output terminal OUT is slidably engaged with the variable resistor VR. Between the end a and the center tap b of the variable resistor VR, a compensating capacitor C1 for compensating a high frequency range and a resistor R1 which are connected in series are connected in parallel. Between the center tap b and the other end c of the variable resistor VR, a compensating capacitor C2 for compensating a low frequency range and a resistor R2 which are connected in series are connected in parallel.
In operation, when the slider d is slid on the variable resistor VR between the tap b and the end c, the frequency characteristic is controlled to have a constant output level in low and high frequency ranges with respect to the middle frequency range. On the other hand, when the slider d slides on the variable resistor VR between the end a and the tap b, as a resistance between the tap b and the slider d increases, a resistance between the end a and the slider d gradually reduces. Thus, the frequency characteristic becomes flat as a whole.
The volume control system having a mechanical tap can be replaced with an integrated circuit system, so that the same characteristic is electronically obtained to achieve an electronic volume controller.
FIG. 10 shows a frequency characteristic of the aforementioned conventional system, taking the volume position as a parameter. It will be seen that at a low volume position (attenuation of the volume is large), low and high frequency ranges are increased compared with the middle frequency range. At a high volume position, the frequency is approximately flat.
In such a characteristic of the conventional system, the low and high frequency levels in the small volume are insufficient with respect to the characteristic of auditory sensation of FIG. 8. In particular, in a room of a car having a small space with noises, a problem that insufficiency in low and high frequency ranges is increased rises. Furthermore, if the volume level is lowered from the tap position, the frequency characteristic is not gradually changed. Thus, as shown in FIG. 10, in curves of attenuation of volume of xe2x88x9230 dB, xe2x88x9235 dB, and xe2x88x9240 dB, the frequency characteristics are not changed. As a result, insufficiency in the low and high frequency ranges is increased.
An object of the present invention is to provide a loudness volume control system where even if the volume position is low, insufficiency of the characteristic in low and high frequency ranges is eliminated with a simple structure.
According to the present invention, there is provided a loudness volume control system comprising a volume controller having a tap, at least one difference compensation circuit connected to the volume controller in series, the difference compensation circuit being arranged so as to independently control a bass range and a mid-range in accordance with an amount of volume control by the volume controller.
The difference compensation circuit is arranged so as to attenuate a bass range level or a treble range level, or to increase a mid-range level in a first level range from a maximum volume level to a volume level of the volume controller, thereby providing a frequency characteristic having a small level changing quantity, and so as to attenuate the mid-range level, or to increase the bass range,level or the treble range level in a second level range lower than the volume level.
The difference compensation circuit may be provided to attenuate only the bass range, or only the treble range, or the bass range and treble range, and increase the mid-range.
The difference compensation circuit comprises a voltage control amplifier and an external CR network.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.